Randomized, controlled, multicenter clinical trial, in which subjects randomized to one group will have active intervention, while subjects randomized to the control group will be closely monitored and offered treatment at the earliest sign of Insulin-Dependent Diabetes Mellitus (IDDM). Type I or IDDM arises in genetically predisposed individuals as a consequence of immune mediated destruction of the pancreatic islet insulin secreting beta-cells. The onset of clinical symptoms of diabetes represents the end point of a chronic progressive decline in beta-cell function, and it appears only when the majority of beta-cells have been lost. Since IDDM develops insidiously, often years after the induction of the pathogenic immune-mediated destructive process, it can be predicted using immunological markers and tests of insulin secretion. The Diabetes Prevention Trial of Type-1 Diabetes (DPT1) has been designed to test whether intervention during the prodromal period of the disease can delay its clinical onset.